Introduction to Nuclear Power

The controversy surrounding nuclear power is the combined result of pragmatic concerns regarding nuclear waste, the potential consequences of accidents (such as Chernobyl and Three Mile Island), and uneducated / irrational views of a pending nuclear incident of the magnitude of Hiroshima and Nagasaki. Despite its controversy, nuclear power is being reexamined in the context of energy market realities. These include:

• Projections in the U.S. alone call for the addition of over 300 electricity generating facilities over the next 30 years to meet growing demand and replace aging units,
• The commitment to reduce CO2 emissions attributed to fossil fuel generation, and
• Questions regarding the viability of other alternative energy sources (e.g. solar, wind, geothermal, and hydro) to meet the peak load demand.

The fact that nuclear technology offers a relatively low cost and low carbon emission solution warrants greater focus on educating the public and affecting a permanent solution to the nuclear waste challenge. This article removes some of the mystique surrounding nuclear energy and encourages the U.S. to accelerate its reentry into the nuclear market, particularly when considering the following:

• There are over 430 operating nuclear plants in 31 countries providing 15 percent of the world’s energy.
• According to the Nuclear Energy Institute (NEI), France receives 77 percent of its electricity from nuclear power and even Lusitania receives 65 percent.
• The U.S., with 104 operating nuclear power plants receives 20 percent of its electricity from nuclear power.

There exists an opportunity for the U.S. to make a major impact in this area. Public objections will diminish as one better understands that nuclear power plants do not operate significantly differently than coal-based power plants, but for the source of heating (nuclear fission) and resulting CO2 emissions (which are virtually nonexistent for nuclear plants).

Nuclear Reactor Operations – The Basics

The basis for nuclear power is induced fission of uranium-235 (U-235) through the introduction of a free neutron into its nucleus. As the nucleus captures the neutron, it splits into 2 lighter atoms which in turn, throw of 2 or 3 new neutrons initiating a chain reaction which releases 200 million electron volts per U-235 atom. The compounding effect of this action on one pound of uranium, enriched to contain 2 or 3 percent more U-235, is equivalent to one million gallons of gasoline. Similarly, another fissionable material, plutonium-239 can be used, created by bombarding U-238 with neutrons, with similar effect.

It is important to differentiate this process from weapons applications, where the amount of enrichment required for weapons-grade uranium is 90 percent instead of 2-3 percent. The chain reaction described above entails U-235 atoms, but necessarily includes these atoms as part of a mass of uranium, as the free neutrons from each fissionable event must hit another U-235 nucleus and cause it to split. The number of these free neutrons that actually hit another U-235 nucleus determines whether critical, subcritical or supercritical mass has been met:

• Critical Mass is achieved when, on average, one of the free neutrons hits another U-235 nucleus and causes it to split.
• Sub critical Mass is achieved when, on average, less than one of the free neutrons hits another U-235 atom. In this case, induced fission will eventually end as will the source of power.
• Super critical Mass is achieved when, on average, more than one of the free neutrons hits another U-235 atom, thereby causing the reactor to heat up.

In the case of a nuclear weapon, the mass of uranium is extremely super-critical so that all of the U-235 atoms split in a microsecond. However, in a nuclear reactor, the core needs to be only slightly super-critical, thus allowing the operators to raise and lower the temperature of the reactor, through the use of control rods. Consequently, controlling the criticality of uranium is key to the safe and controlled operation of a nuclear reactor, which requires attention to:

• The amount of enriched U-235 (2 pounds) or P-239 (10 ounces) in the mass, and
• The shape of the mass, a sphere being the optimal shape.

The enriched uranium is formed into small, usually inch-long, pellets, which are in turn arranged into long rods. These rods are collected into bundles which are submerged in water inside a pressure vessel where the water acts as a coolant. As previously stated, the submerged bundles are slightly super-critical. Left alone, they will eventually overheat and melt. The aforementioned control rods, designed to absorb neutrons, are inserted into these bundles with the ability to be mechanically raised and lowered, thus controlling the rate of the nuclear reaction:

• When more heat is appropriate, the operator raises the control rods out of the uranium bundle, absorbing fewer neutrons.
• To create less heat, the operator merely increases the absorption of neutrons by lowering the control rods.
• If the control rods are lowered completely into the uranium bundle, the reactor will shut down completely. This is done in the case of an accident or if the utility wants to change the fuel.

The remainder of the plant operation is similar to the basic cycle of other power plant operations. The heated water is transformed into steam and drives the turbine, spinning a generator that produces power. However, given the realities of radioactivity, there are some elements outside the plants that differentiate them from fossil plants.

Outside the Nuclear Reactor

There are a number of features that also differentiate a nuclear power plant from the more conventional fossil fuel power plants. These include:

• There is a concrete liner around the reactor’s pressure vessel that acts as a radiation shield, which is housed within a larger steel containment vessel. This vessel provides a barrier to prevent leakage of radioactive gases or fluids from the plant.
• An outer concrete building, designed to withstand earthquakes and even the crash of a jet airliner, offers a final layer of protection in the event of an accident. This secondary structure, providing added assurance that radiation / radioactive steam will not escape into the atmosphere, was not part of the design of the plant in Chernobyl.
• Each nuclear power plant has a control room, where operators continuously monitor the nuclear reactor and remotely initiate actions if there are any developing unsafe conditions.
• Given the sensitivity of nuclear materials, all nuclear facilities employ added security.

As basic as nuclear power operations are, and despite the efforts to incorporate safety into the design and operations of these plants, there is understandably significant controversy around the viability of nuclear power as part of the permanent energy solution. The following section explores the more obvious pluses and minuses related to this technology.

Arguments For and Against Nuclear Power

Nuclear Power offers a number of advantages as well as its share of disadvantages as a energy source. Given the world’s reliance on energy for economic prosperity and quality of life, there appears to be little option but to explore how to accentuate the positives and manage the risks inherent to this technology.

First, the positives:

• According to the Nuclear Energy Institute (NEI), if replaced by fossil stations, the power produced by nuclear plants worldwide would produce over 2 billion metric tons of CO2 annually.
• Coal-fired plants actually emit more radioactive gases into the atmosphere than a properly functioning nuclear power plant.
• The cost of nuclear power is not impacted by the fluctuations we experience with the price of oil and gas.

And, the negatives:

• Mining and purifying uranium is not a clean process and the transporting of nuclear fuel to and from nuclear power plants presents a contamination risk.
• Typically, a nuclear power plant generates 20 metric tons of nuclear fuel annually. This is referred to as high-level radioactive waste and a significant amount of low-level radioactive waste exists in the form of radiated parts and equipment. Storage systems for this waste must account for the radiation and heat emitted by this material, which over an extended period of time will corrode any container and prove harmful to the environment.
• Whether high or low level radioactive waste, the decay of these materials to safe radioactive levels ranges from centuries to tens of thousands of years. Technical solutions for storage exist, but there remain political and economic barriers to overcome. In the interim, the industry has adopted measures to maintain, monitor, and guard these used materials, but not without some degree of risk and added costs.
• Accidents have been few and far between. However, their results are catastrophic, as evidenced at Chernobyl. However, had Chernobyl been properly designed and operated, the disaster would have been significantly mitigated.

Our view is that properly designed and safely operated nuclear power plants offer significant benefits in terms of scalability and our drive to maintain a continually cleaner environment. Without it, the more limited renewable technologies cannot keep pace with the increased demand for energy (and more specifically electricity). As the main objections focus around issues of design and operation and the safe storage of radioactive waste; all of these problem areas have solutions. The U.S. is in a unique position to exert leadership in this area because (1) there is significant room to increase the role of nuclear power in its current energy portfolio, (2) it has maintained a consistent focus on operational safety of nuclear power, and (3) there are long-term storage solutions that merely need to be acted upon that can set an example for the rest of the world.